Lawn fertilizer and lime are complementary additions. Lawns are fertilized to add necessary nutrients that grass needs to grow well and maintain a rich, green color. Lime is not a fertilizer; it is a soil amendment that is added to soil to make it easier for grass to accept and use the nutrients added in fertilizer.
The three main ingredients in fertilizers are nitrogen, phosphorus and potassium. The contents of commercial fertilizers are expressed in three numbers that give the percentage by weight of N (nitrogen), P (phosphorus) and K (potassium). Secondary nutrients include calcium, magnesium and sulfur. Plants also need trace amounts of copper, iron, manganese and zinc. Lawn fertilizers include more nitrogen, needed for grass to grow and maintain its rich, green color. The ability of a lawn to accept the nitrogen and other nutrients depends largely on the pH of its soil.
Soil pH and Lime
The pH number of soil measures hydrogen ions in numbers ranging from 1 to 14 with 7 being neutral. Acidic soils have a pH under 7; alkaline soils have a pH higher than 7. Most lawn grasses more easily absorb nitrogen and other nutrients at a soil pH between 6.5 and 7. Lime is added to soil to correct its pH to achieve this optimal level. A soil test can be arranged through most agricultural extension centers to determine if lime needs be added to a lawn and how much is needed.
Benefits of Lime
Lime helps correct acidic soil that can cause aluminum, iron and manganese in fertilizers to be toxic. Lime helps make phosphorus, copper and zinc more available to soil. It also increases the activity of bacteria in the soil that help decay organic matter. Soil with a good pH is usually more porous, helping the soil absorb and hold moisture and making more air available to grass roots.
Lime for Lawns
The lime most often used to amend lawns is calcium carbonate, CaCO3, made of ground limestone. Calcium carbonate is given a CCE rating that stands for calcium carbonate equivalent; pure calcium carbonate is given a CCE rating of 100. Dolomitic limestone that contains magnesium is recommended for lawns that are deficient in magnesium. Fine grinds of calcium carbonate correct soil pH more quickly than coarse grinds, but they can blow in the wind and are more likely to cause lime burns on the grass. Garden centers sell lime in the form of pellets that do not blow in the wind and that can be scattered by hand.
Silt or clay soils require more lime than light, sandy soil; too much lime can cause lawns to burn and turn yellow or brown. A soil test will determine how much lime should be applied, but agronomists at West Virginia University do not recommend single applications of more than 150 lbs. per 1,000 square feet.
Lime moves slowly through soil--up to two years to move 2 inches. It does not move horizontally, so it needs to be applied over the entire area. The best time to add lime to soil is before a lawn is planted. If it is added to an established lawn it is best applied to dry grass in the fall, winter or early spring. Lime is usually applied several times over a period of weeks, and lawns should be watered after each application.